diff --git a/sendfile_std.go b/sendfile_std.go
index 1447b6db..92278305 100644
--- a/sendfile_std.go
+++ b/sendfile_std.go
@@ -41,7 +41,7 @@ func (c *Conn) Sendfile(f *os.File, remain int64) (written int64, err error) {
 			if nw < 0 {
 				nw = 0
 			}
-			if c.p.g.onWrittenSize != nil && n > 0 {
+			if c.p.g.onWrittenSize != nil && nw > 0 {
 				c.p.g.onWrittenSize(c, nil, nw)
 			}
 			remain -= int64(nw)